Area Forecast Discussion
Issued by NWS La Crosse, WI

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000
FXUS63 KARX 090444
AFDARX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LA CROSSE WI
1144 PM CDT TUE JUL 8 2014

.SHORT TERM...(THIS EVENING THROUGH WEDNESDAY)
ISSUED AT 308 PM CDT TUE JUL 8 2014

MAIN SHORT TERM FORECAST CONCERNS ARE ON SHOWER CHANCES THROUGH
WEDNESDAY.

CURRENTLY AS OF 20Z...WATER VAPOR LOOP AND RAP 500MB HEIGHT ANALYSIS
SHOWED RIDGING OVER THE WESTERN U.S. INTO SOUTHWEST CANADA...WHILE
TROUGHING WAS IN PLACE FROM HUDSON BAY INTO THE WESTERN GREAT LAKES
REGION. TWO MAIN SHORTWAVES OF NOTE WERE OVER NORTHERN WI AND
CENTRAL MANITOBA. COOL AIR ALOFT WITH THE SHORTWAVES ARE COMBINING
WITH DAYTIME INSTABILITY TO PRODUCE SHOWERS AND A FEW THUNDERSTORMS.
THAT COOL AIR ALOFT WAS EVIDENT EVEN AT 850MB WITH 12Z SOUNDINGS AT
MPX AND GRB OF 12C AND AT INL OF 9C. THESE COOL 850MB TEMPS HAVE
HELD TEMPERATURES MOSTLY IN THE 70S TODAY. DEWPOINTS HAVE MIXED DOWN
INTO THE 50S THANKS TO A FLOW OF DRY AIR ON BREEZY NORTHWEST WINDS.
THIS DRY AIR OVER THE NORTHERN PLAINS HAD PRECIPITABLE WATER VALUES
OF 0.5-1 INCH PER 12Z SOUNDINGS...OR 50-100 PERCENT OF NORMAL.

MAIN FOCUS FOR THE SHORT TERM IS ON THE SHORTWAVE OVER CENTRAL
MANITOBA. MODELS PROG THIS SHORTWAVE TO ROUND THE TROUGH AND CROSS
NORTHERN WI BETWEEN 03-09Z. ALTHOUGH THE SHORTWAVE IS COMING ACROSS
DURING THE NOCTURNAL HOURS...CANNOT RULE OUT A FEW SHOWERS WITH IT
GIVEN THE STRENGTH OF THE WAVE. SEEMS LIKE THE TRACK OF THE WAVE
WILL KEEP THE MAJORITY OF THE SHOWER ACTIVITY NORTHEAST OF THE
FORECAST AREA...BUT JUST IN CASE DID HOLD ONTO A 20 PERCENT CHANCE
ACROSS TAYLOR IN THE EVENING HOURS.

COOLER AIR ALOFT LOOKS TO LINGER INTO WEDNESDAY FOR LOCATIONS
ALONG/NORTHEAST OF I-94...AIDED BY THE TAIL END OF THE SHORTWAVE
COMING ACROSS TONIGHT HANGING BACK. IN FACT...850MB TEMPS ARE
PROGGED ABOUT 1C COOLER ON WEDNESDAY COMPARED TO TODAY...RANGING
FROM 9-11C. THE COOL AIR ALOFT COMBINED WITH DAYTIME HEATING AND
EVAPOTRANSPORATION COULD BE ENOUGH TO SPARK A FEW MORE SHOWERS
ALONG/NORTHEAST OF I-94. THUS...HAVE MAINTAINED THE CHANCES THAT
WERE INTRODUCED LAST NIGHT.

EXPECT DRY WEATHER OUTSIDE OF THE AFOREMENTIONED PRECIPITATION
CHANCES...WITH PERSISTENT DRY ADVECTION FROM THE NORTHWEST AIDING AN
OVERALL GRADUAL FALL IN DEWPOINTS THE NEXT 24 HOURS.

.LONG TERM...(WEDNESDAY NIGHT THROUGH TUESDAY)
ISSUED AT 308 PM CDT TUE JUL 8 2014

LONG TERM HIGHLIGHTS INCLUDE COOL WEDNESDAY NIGHT...POTENTIAL
CONVECTION THURSDAY NIGHT THROUGH THE WEEKEND...AND A MUCH BELOW
NORMAL AIRMASS FOR EARLY NEXT WEEK.

WEDNESDAY NIGHT AND THURSDAY FEATURES BUILDING UPPER RIDGING AHEAD
OF AN UPPER TROUGH CROSSING SOUTHWEST CANADA. SUBSIDENCE UNDER THIS
BUILDING RIDGE...HIGH PRESSURE MOVING IN PLACE AT THE SURFACE AND
PRECIPITABLE WATER PROGGED IN THE 0.5-1 INCH RANGE WILL RESULT IN
DRY CONDITIONS. THE CONDITIONS ALSO FAVOR GOOD RADIATIONAL COOLING
FOR WEDNESDAY NIGHT. GIVEN MOISTURE POOLING IN SMALLER VALLEY AND IN
THE CRANBERRY BOG AREAS...THE COOLER NIGHT WILL LIKELY LEAD TO SOME
FOG IN THESE LOCATIONS. THE AIR MAY BE TOO DRY TO ALLOW THE
MISSISSIPPI TO FOG. ANOTHER MONTH FROM NOW WHEN WE HAVE A LONGER
NIGHT...THIS WOULD BE A DIFFERENT STORY. TEMPERATURES SHOULD END UP
WARMER TOO ON THURSDAY AS 850MB TEMPS BEGIN TO CLIMB TO 12-14C BY
00Z.

THE WEATHER THEN GETS A BIT MORE ACTIVE THURSDAY NIGHT AND FRIDAY
DUE TO A SHORTWAVE RIDING THROUGH THE ZONAL FLOW OVER THE NORTHERN
PLAINS. MODELS HAVE HAD A CONSISTENT SIGNAL OF THIS SHORTWAVE
INDUCING A STRONG 850MB MOISTURE TRANSPORT ZONE FROM THE CENTRAL
PLAINS INTO OUR REGION. GENERAL MODEL CONSENSUS IS FOR A CONVECTIVE
COMPLEX TO FORM ON THE NOSE OF THIS MOISTURE TRANSPORT IN IOWA
THURSDAY NIGHT...WHICH CORFIDI VECTORS WOULD SUGGEST A SOUTHEAST
MOVEMENT. ALTHOUGH THIS COMPLEX MAY STAY AWAY FROM THE AREA...IT
APPEARS THERE SHOULD BE ENOUGH OF THIS MOISTURE TRANSPORT AIMING UP
AT US TO COMBINE WITH DPVA FROM THE SHORTWAVE TO GENERATE SHOWERS
AND THUNDERSTORMS FARTHER NORTH. THUS...HAVE MAINTAINED HIGH
PRECIPITATION CHANCES...50-70...CENTERED ON THE 06-18Z FRIDAY
PERIOD. THIS PRECIPITATION AND ASSOCIATED CLOUDS WILL HELP KEEP IT
COOLER ON FRIDAY TEMPERATURE WISE...DESPITE 850MB TEMPS RISING TO 14-
17C. DEWPOINTS ARE GOING TO BE ON THE RISE...THOUGH...MAKING IT FEEL
MORE MUGGY.

FOR FRIDAY NIGHT INTO THE WEEKEND...ITS A VERY UNCERTAIN FORECAST.
THERE IS VERY GOOD MODEL AGREEMENT ON UPPER TROUGHING DROPPING SOUTH
FROM CENTRAL CANADA INTO THE WESTERN GREAT LAKES REGION...BUT
DETAILS WITHIN THE TROUGH VARY FROM MODEL TO MODEL. THESE DETAILS
IMPACT FRONTAL BOUNDARIES DROPPING THROUGH THE REGION AND THUS WHERE
CONVECTION CAN FIRE. CERTAINLY APPEARS THAT WE COULD DEAL WITH A
COUPLE BOUTS OF CONVECTION...BUT FOR NOW HAVE TO BLANKET MUCH OF THE
WEEKEND WITH 20-40 PERCENT CHANCES UNTIL DETAILS CAN SORT THEMSELVES
OUT. SHOULD BE A GENERAL COOLING TREND HEADING INTO
SUNDAY...THOUGH.

THE FORECAST BECOMES MORE CERTAIN EARLY NEXT WEEK WITH THE ECMWF AND
GFS NOW IN-SYNC HAVING AN ANOMALOUSLY DEEP UPPER LOW DROP DOWN INTO
THE LAKE SUPERIOR REGION BY MONDAY EVENING. THE ECMWF AND GFS
ENSEMBLES ARE ALSO TRENDING TOWARDS THIS SCENARIO. BACKING TRACKING
THE UPPER LOW...IT ORIGINATES RIGHT NOW FROM THE ARCTIC...A
SITUATION SIMILAR TO WHAT WE SAW DURING THE WINTER. THUS...850MB
TEMPS TANK EARLY NEXT WEEK...DROPPING TO AS LOW AS +2C AT 12Z
TUESDAY. THE 08.00Z ECMWF STRUGGLES TO GET LA CROSSE UP TO 65 FOR
TUESDAY...WHICH WOULD BREAK THE RECORD MINIMUM HIGH TEMPERATURE OF
68 SET IN 1962. DID NOT GO THAT COLD YET SINCE IT IS 7 DAYS
OUT...BUT KEPT IT MUCH BELOW NORMAL WITH HIGHS OF UPPER 60S TO LOW
70S. ALSO HAVE SOME LOW CHANCES OF RAIN GIVEN THE COOL AIR
ALOFT...THOUGH ITS POSSIBLE THE AIR WILL BE DRY ENOUGH TO PREVENT
ANY PRECIPITATION.

&&

.AVIATION...(FOR THE 06Z TAFS THROUGH 06Z WEDNESDAY NIGHT)
ISSUED AT 1144 PM CDT TUE JUL 8 2014

STILL SOME CLOUDS FLOATING AROUND OVER CENTRAL AND NORTHERN
WISCONSIN ALONG WITH NORTHWEST MINNESOTA LATE THIS EVENING.
HOWEVER...SATELLITE TRENDS SHOW THESE CONTINUE TO SLOWLY
DISSIPATE AND DO NOT THINK THEY WILL AFFECT EITHER TAF SITE
THROUGH THE REMAINDER OF THE NIGHT. THE 09.00Z NAM CONTINUES TO
SHOW SATURATION AT THE SURFACE OCCURRING LATE TONIGHT AT KLSE WITH
THE WINDS QUICKLY INCREASING ABOVE THE SURFACE AND THIS SHOULD BE
ENOUGH TO KEEP ANY FOG FROM FORMING. THE NAM ALSO STILL SHOWS SOME
WEAK PV ADVECTION IN THE 500-300 MB LAYER COMING ACROSS THE AREA
LATE WEDNESDAY AFTERNOON BUT THE LATEST BUFKIT SOUNDING FOR KLSE
SHOWS SUBSIDENCE OCCURRING. THE NAM STILL PRODUCES SOME
SHOWERS...BUT THESE ARE OVER NORTHEAST WISCONSIN IN AGREEMENT WITH
THE 08.12Z ECMWF AND 09.21Z SREF AND DO NOT PLAN TO INCLUDE ANY
SHOWERS IN EITHER TAF.

&&

.HYDROLOGY...
ISSUED AT 308 PM CDT TUE JUL 8 2014

WATER LEVELS CONTINUE TO FALL ON THE MISSISSIPPI RIVER. WE ARE
EXPECTING ALL THE RIVER FORECAST POINTS WITHIN THE ARX FORECAST AREA
TO FALL BELOW FLOOD STAGE BY THURSDAY FROM NORTH TO SOUTH. FOR
THE CURRENT AND FORECAST RIVER LEVELS...SEE OUR INTERNET PAGE AT
WWW.WEATHER.GOV/LACROSSE.

&&

.ARX WATCHES/WARNINGS/ADVISORIES...
WI...NONE.
MN...NONE.
IA...NONE.
&&

$$

SHORT TERM...AJ
LONG TERM...AJ
AVIATION...04
HYDROLOGY...DAS/AJ



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